Dendritic cells (DC) have a central role in the induction and polarization of Th subsets. However, the precise molecular determinants of Th2 polarization have not been defined. This project seeks to address this gap in knowledge by focusing on signaling events not previously implicated in this context in DC: ones mediated by the heterotrimeric (???) GTP binding proteins Gs, which stimulates and Gi, which inhibits the synthesis of cAMP. We have recently engineered mice that have a CD11c-specific deletion of Gnas, i.e., CD11c-Cre Gnasfl/fl (?CD11c), the gene that encodes Gs. Compared to wild-type (WT) mice, DC of these mice generate less cAMP in response to Gs activation. Furthermore, these mice have an unexpected phenotype: they are atopic and develop spontaneous (i.e., without immunization) Th2 responses and progressive allergic asthma. Bone marrow-derived DC (BMDC) from the ?CD11c mice have altered gene expression, including of numerous genes that correspond to ones identified in genome-wide association studies (GWAS) of asthmatic patients. Thus, multiple types of data that we have accrued suggest that this new animal model is predictive of what occurs in human atopy and allergic asthma. We hypothesize that: a) the imbalance between Gs and Gi expression and signaling in DC and the resultant decrease in formation and action of cAMP, induces a pro-Th2 phenotype and b) studies of this imbalance will uncover new ways to regulate Th2 responses and related pathologies, in particular allergic asthma, in mice and potentially humans. This revised application is focused on a previously unappreciated type of regulation of DC phenotype and one that we believe has important implications for human disease. The project has 4 Specific Aims (SAs). In SA-1 we will define the impact Gs/Gi signaling imbalance in CD11c on Th2 development and the allergic phenotype in genetically engineered mice with alterations in the expression or activity of the G? proteins. In SA-2 we will determine the role of different CD11c+ DC subsets from the lungs in the pro-Th2 bias observed in mice mentioned above. In SA-3 we will identify Gi- and Gs-coupled GPCRs in DC as targets to regulated Th2 induction, and in SA-4 we will identify Gs/Gi-related molecular events that determine the pro-Th2 DC phenotype. Overall the proposed experiments are designed to reveal a newly recognized pathway of Th2 induction and new facets of DC and GPCR biology. An important outcome would be the discovery of GPCR/G-protein-related drugs that block Th2 induction and hence to inhibit atopic and allergic diseases, in particular allergic asthma.